1. Field of the Invention
The present invention relates to a multilayer color photographic material, more specifically, the invention relates to a silver saving multilayer color photographic material having a low content of light sensitive silver halide as compared to ordinary color photographic materials. In particular, the invention relates to a silver saving multilayer color photographic material which can optically record sound images.
2. Description of the Prior Art
Various attempts have recently been proposed to conserve silver resources and to reduce the production cost of photographic materials. For example, it is known to increase the amount of dyes by subjecting the silver formed in color development to halogenation bleaching and thereafter again subject the silver halide thus formed to color development (see, e.g., U.S. Pat. Nos. 2,439,901, 2,623,822, 2,814,565, and 3,372,028).
Furthermore, various color intensification methods have been proposed as other methods of conserving the silver contained in photographic materials. For example, according to the disclosure in U.S. Pat. No. 3,674,490, the oxidation reaction is accelerated by a peroxide such as hydrogen peroxide with image-wise distributed nuclei as a catalyst to form dyes and to form color images. In this case, as the nuclei exist as a catalyst, the amount thereof may be very small, and, thus, when silver is used as such nuclei in photographic materials, the desired color density can be obtained using a far smaller amount of silver salt than in conventional gelatino silver salt emulsions. In the method of this patent, the peroxide is used in an intensification step practiced after development, or, typically, in a color development step.
On the other hand, in U.S. Pat. No. 3,765,891, a new color intensification method is described in which dye images are formed by an oxidation-reduction reaction with a cobalt(III) complex salt such as hexammine cobalt(III) chloride using image-wise distributed nuclei as a catalyst. Also, in Japanese Patent Application No. 128,327/74, there is described a method of intensifying color images by causing at least one member selected from the group consisting of a chlorite, chlorous acid, and an aqueous chlorine dioxide solution to act on image-wise distributed nuclei in the presence of a reducing agent. In this case, an alkali metal salt or an alkaline earth metal salt of chlorous acid is used as the chlorite.
According to the methods described above, when exposed silver halide emulsions containing color couplers are brought into contact with a color developing agent and an oxidizing agent as described above, such as, for example, a peroxide, a cobalt (III) complex salt, or a chlorite, the color developing agent is oxidized in the presence of silver as a catalyst and the oxidized color developing agent causes a coupling reaction with the color couplers to form dye images while the oxidizing agent is reduced.
In any case described above, since silver is present solely as a catalyst, the amount of silver may be very small, and, hence, the desired color density can be obtained using a far smaller amount of silver salt than the amount of silver salt used in conventional color photographic materials.
Accordingly, the stoichiometrically equivalent relationship which exists in the oxidation-reduction system between a color coupler and silver in conventional color photographic techniques does not exist in such new color photographic techniques as indicated above. That is, two mols or four mols of silver are required to form one mol of dye in conventional techniques, but in the case of employing the aforesaid color intensification technique, the amount of silver used may be far smaller than the aforementioned stoichiometric amount of silver. In other words, by using a larger amount of color coupler than the stoichiometric amount thereof in the case of considering silver the standard element for stoichiometric calculations, the amount of silver contained in color photographic materials can be reduced. For example, in U.S. Pat. No. 3,834,907 there is described a method of obtaining dye images having a high color density by exposing light sensitive silver salt emulsion layers containing excess color couplers, i.e., excess to the stoichiometric amounts thereof, by more than 40 mol%, preferably by more than 70 mol%, with silver as the standard element, and then bringing the exposed silver salt emulsion layers into contact with a color developing agent and an oxidizing agent such as a hexa-coordinate cobalt(III) complex. In this case, the hexa-coordinate cobalt(III) complex is reduced to a cobalt(II) complex by the catalytic action of the silver and at the same time dye images are formed.
However, in a color photographic material having an optical sound track (as will be explained later), such as a color reversal print film, a color reversal film, or a color print film, it is undesirable to excessively reduce the coated amount of silver of the color photographic materials to obtain the desired optical density (infrared density).
The reproduction of sound in an optical recording system for color print films, color reversal films, color reversal print films used in the field of cinema or television is performed by the steps of converting a sound signal recorded in the film as a density pattern or area pattern into a light signal, converting the light signal into an electric signal by means of a light receptor, and further converting the electric signal into a sound signal. In the sound reproducing system, photoelectric tubes possessing various optical characteristics are used as the light receptor. Among these photoelectric tubes, the most frequently used one is an S-1 type photoelectric tube having a maximum spectral sensitivity at the wavelength of about 800 m.mu. in the infrared region (see, e.g., Ardrin Cernwell Clyne, Color Cinematography, 593 (1951)).
On the other hand, in conventional color photographic materials subjected to subtractive color processing, the main absorptions of dyes formed by the coupling reaction of the oxidation product of a color developing agent (such as a p-phenylenediamine) and color couplers are all in the visible region which does not coincide with the spectral characteristics of the above indicated photoelectric tube. Therefore, if only such coupled dye images are relied upon, the sound output is weak and practically unuseable. Therefore, in order to reproduce sound in color photographic materials, the color photographic film is usually treated in a processing step in such a manner that a silver image or a silver sulfide image is formed on a sound track and the silver image or silver sulfide image thus formed in the infrared region is utilized for sound reproduction. The infrared density (transmission density) in this case is usually about 0.8 to 1.6.
The sound track in a color print film is formed by, for example, the treatment as described in the Journal of the Society of Motion Picture and Television Engineers, Vol. 61, 667-701 (1953).
By the method described in the aforesaid journal, the color images in the picture image areas and the sound images in the sound track areas of the color print film are simultaneously subjected to color development in a color development bath.
In a first fixing bath, unexposed silver is removed and, in a bleaching bath, developed silver in the development step is re-halogenated. In the sound development step, silver halide is converted into a silver image only in the sound track areas by selectively applying a viscous sound developer to the sound track areas. In a second fixing bath, silver halide in the image areas is fixed and removed, and, further, in a stabilization bath, dye images are stabilized. The density in the infrared region of the silver image formed on the sound track is mainly utilized for the reproduction of sound.
The sound track in reversal color print film is formed by, for example, the method as described in Journal of the Society of Motion Picture and Television Engineers, Vol. 76, 1198-1201 (1967). In this case, a sound image of silver is formed when the original of the sound is a negative image while a sound image of silver sulfide is formed when the original of the sound is a positive image.
In the production of sound tracks for color films, the step of forming silver or silver sulfide images is required, as stated above. The reason for forming a sound track composed of a silver image or silver sulfide image is that the spectral sensitivity characteristics of a photoelectric tube used for the reproduction of sound have a sensitivity maximum in the infrared wavelength region, but, on the other hand, dyes formed by a color development process do not have sufficient density in this wavelength region, as described before.
Therefore, in order to form an optical sound track on a color film, the film is required to contain silver therein.
In another method of forming an optical sound track containing silver on a sound recording area, a silver bleach inhibitor is applied as described in, for example, U.S. Pat. No. 3,705,803 and Japanese Patent Application (OPI) No. 24,431/74 and 87,727/73; such a method is preferably employed for forming an optical sound track on the color photographic material of this invention.
Thus, if the amount of silver in the coated layers of color photographic materials such as color reversal print films, color reversal films, color print films, etc., is excessively reduced, the optical density (infrared density) of the optical sound track formed on the color photographic material becomes insufficient.
Furthermore, when a multilayer color photographic material having an extremely reduced amount of silver in the coated emulsion layers is subjected to a color intensification development processing, sometimes the color balance of color images formed is lost by differences in coupling rates of color couplers in the emulsion layers, a development inhibition action by development inhibitor releasing compounds, etc., which results in unsatisfactory photographic characteristics.